Methods of manufacturing pneumatic tires generally include building a green tire upon an inflatable bladder. The green tire is then placed into a mold and cured while the green tire is subjected to pressure from a curing bladder. The former bladder is typically referred to as a tire building bladder while the later typically referred to as a tire curing bladder.
Tire building bladders are typically not subjected to significant stresses, and the primary design feature is often related to preventing adhesion between the bladder and the green tire components. Historically, these tire building bladders have been constructed from natural rubber, and the bladder is typically modified with a release coating or layer, such as those deriving from silicone oils or silicone rubbers.
On the other hand, tire curing bladders are subjected to significant stresses. During the curing process, the bladder, which is adapted to seat within the mold, is inflated inside the green tire. The green tire is therefore forced to flow into the mold, which thereby causes the tire to take on the configuration of the mold. The bladder is often also used to transfer heat to the green tire through a fluid, such as steam, that is circulated through the bladder. After the curing process, the bladder is deflated and the tire is removed from the mold. These bladders are therefore subjected to repeated cycles of inflation and deflation while undergoing severe conditions of heat and pressure. Moreover, to prevent the green rubber from adhering and curing to the bladder, release agents are applied to the bladder surface. To withstand the dynamic, thermal, and chemical conditions to which the bladder is subjected, tire curing bladders are often formed from butyl rubber formulations, which have high resistance to heat and chemical degradation while being very elastic. Nonetheless, the severity of the conditions and stresses experienced by the bladders has a deleterious impact on the bladders. For example, the surface of the bladder can become oxidized, which can result in the cracking of the surface. This can have a deleterious impact on the tire being cured because it introduces surface imperfections where the bladder contacts the tire. Also, where air or steam is released through holes within the bladder (from pinholes to catastrophic failure of the bladder), the tire can experience not only aesthetic damage, but structural damage as well. As a result, the service life of bladders can be relatively short.
There is therefore a need in the industry to extend the life of tire curing bladders.